When Dave Clark launched Sounder at Heart in August 2008, he had little inkling how significant a role it would play in forming the fan culture of a team still months away from its first Major League Soccer campaign.

Clark’s ambitions were modest. He simply wanted an outlet for his own writing and to provide a forum for like-minded Seattle soccer fans. Clark harbored no illusions of using the website to get rich. His initial goal was to make enough to pay for his season tickets at what was then called Qwest Field, to “cover the cost of my hobby,” as he puts it.

His first 15 months running the site, he made $56 in ad revenue.

And yet there proved to be something quietly revolutionary about his concept, which would carry over when it was folded into SB Nation’s network a year-and-a-half in. Years before newspapers and other traditional media outlets hit upon the concept of engaging with readers, on the value of strong comments sections and the feeling...